The invention relates to fuel supply systems for high efficiency gas turbine engines for aircraft propulsion and particularly to a new and improved dual fuel manifold system and method for operating same wherein each manifold supplies fuel to a portion of the fuel injectors and one of the manifolds has a cutoff valve between it and the fuel control.
Recent improvements in aircraft jet engine technology with respect to fuel efficiency have been too numerous to mention. Improvements in the various components and systems, such as the compressor, turbine, and controls, have yielded significant reductions in the amount of fuel required during typical flight mission cycles. One effect of the reduced fuel requirements is to lower the combustor operating fuel to air ratio to levels approaching the lean stability limit conventionally know as the blowout limit. The reduced fuel requirement exists during steady-state and transient operating conditions of the engine. Under certain flight conditions such as during idle descent on a cold day, a period during which the aircraft is reducing its cruise altitude, the combustor of the gas generating portion of the jet engine may experience fuel starvation at one or more fuel injectors. The result may be severe enough to exceed the blowout limit thereby totally extinguishing the combustion process and stopping the engine's operation. Further complicating the design and operation of these highly efficient engines are FAA emission requirements, in particular those directed to preventing high levels of invisible emissions at idle on the ground. The inventors have discovered a jet engine fuel supply system and method of operation to prevent the aforementioned blowout from occurring. The invention also allows the construction and safe operation of larger more efficient high bypass ratio turbofan and propfan engines of both the ducted and unducted type engines. The invention also improves the exhaust emissions of high bypass ratio gas turbine engines from a pollution standpoint thereby helping to meet stringent FAA emission requirements.